A sample contained a mixture of CdS and CoS. The amount of CdS was determined by reacting 8.767 g of the sample with an excess of HCl to release H2S from each compound;
CdS(s) + 2 HCl(aq) ® CdCl2 + H2S(g)
CoS(s) + 2 HCl(aq) ® CoCl2 + H2S(g)
If the sample reacted completely and produced 1931 mL of hydrogen sulfide at 29.82 °C and 759.7 mm Hg, what was the mass percentage of CdS in the mixture?